The rear axle extends left and right from the swing arm outward to the wheels which are mounted to hubs defined by the axle and its unsupported portions beyond the swing arm and before the wheel are subjected to severe bending, even as the axle is under driving rotation, as the vehicle bounces and pitches over rocks, jumps and ruts, often turning the wheel under on landing. To relatively position the axle and the swing arm requires locking means be provided on the axle outwardly adjacent the swing arm, in the very axle shaft area which is subjected to the bending moments.
Typically the locking means has been a nut threaded onto the axle shaft adjacent the swing arm, but the shaft threading induces cracks in the axle shaft under the inevitable severe bending stress, posing safety hazards and necessitating unduly frequent replacement of the axle. In addition hardness of the shaft material has been limited by need to accommodate tendencies to crack at the threads.